Advanced Electronic Signature (AES), Simple (SES) and Qualified (QES): The 3 eIDAS Levels

The advanced electronic signature (AES) is the most widely used level in B2B and the only one to offer a legal presumption of integrity without imposing a smart card on the signer. Alongside the simple signature (SES) and the qualified signature (QES), it makes up the three levels defined by the European eIDAS regulation. Here's how to choose the right level based on the nature of your document, its expected evidential value and the acceptable friction for the signer.

What is an advanced electronic signature (AES)?

The advanced electronic signature is the intermediate level defined by Article 26 of the eIDAS regulation. It must meet four cumulative conditions: (1) be linked uniquely to the signer, (2) allow identification of them, (3) be created from data under their exclusive control, (4) allow detection of any subsequent modification of the signed document. In practice, these conditions are met via strong authentication (email + OTP SMS), a timestamped audit trail and cryptographic hashing of the PDF.

The AES benefits from a legal presumption of integrity and origin that reverses the burden of proof before the judge: it is the person contesting the signature who must prove its falsity, not the signer who must prove its validity. This is what fundamentally distinguishes AES from SES, where reliability is assessed on a case-by-case basis by the judge.

The three levels defined by eIDAS

The European regulation eIDAS (No. 910/2014) organises electronic signatures into three levels, corresponding to progressively increasing requirements in terms of signer identification and strength of evidence. Understanding these levels well allows you to choose the signature adapted to each document, without over-dimensioning the process.

Level 1: Simple electronic signature (SES)

The simple electronic signature is the basic level. It corresponds to any manifestation of electronic consent: a click on "I accept", a checkbox, an initial drawn on a touch screen.

• Requirements: clear consent, minimal identification (email)

• Evidence: weak to medium, varies by provider

• Use cases: quotations, purchase orders, internal agreements, general terms and conditions

• Signer friction: virtually none — the signer does not create an account

SES is sufficient for the vast majority of current commercial exchanges where the risk of dispute is low. It remains legally valid, with the judge assessing the reliability of the process on a case-by-case basis.

Level 2: Advanced electronic signature (AES)

The advanced signature strengthens signer identification and establishes a unique link between them and the document. It is based on four criteria set out in Article 26 of eIDAS:

• it is linked to the signer in a unique manner

• it allows the signer to be identified

• it is created with means that the signer keeps under their exclusive control

• it is linked to the document in such a way as to detect any subsequent modification

In practice, AES goes through two-factor authentication: unique link sent by email + OTP code received by SMS. The final PDF includes timestamping and a detailed audit trail.

• Use cases: employment contract, lease, mandate, commercial contract with stakes, NDA

• Signer friction: low — an SMS code to enter in addition to the email

• Evidence: strong, rebuttable presumption of validity

Level 3: Qualified electronic signature (QES)

The qualified signature is the highest level. It is based on a qualified certificate issued by a qualified trust service provider (QTSP) listed on the trust list of an EU Member State, and on a secure signature creation device (e.g. YubiKey, smart card).

• Legal value: equivalent to a handwritten signature throughout the EU

• Use cases: official deeds, public procurement, certain notarial deeds

• Signer friction: high — face-to-face or KYC video verification

• Cost: significantly higher than SES/AES

For most businesses, QES is rarely necessary on a daily basis. It becomes essential when the law requires it (legal proceedings, certain public procurement) or when the contract has exceptional value.

Quick comparison table

Criterion | Simple | Advanced | Qualified

Identification | Email | Email + OTP SMS | Qualified certificate + identity verification

Legal value | Evidence to be assessed | Presumption of validity | Equivalent to EU handwritten signature

Friction | Virtually none | Low | High

Typical use case | Quotations, purchase orders | Employment contract, lease | Notarial deeds, public procurement

Cost | Low | Moderate | High

How to choose the right level

The simple rule: align the level with the stakes of the document.

• If the document is contested, what is at stake? A few hundred euros or a contract worth tens of thousands?

• Is the relationship with the signer known (established customer) or unknown (first contact)?

• Does the document fall within a legal framework imposing a specific level (e.g. employment contract, lease)?

As a general rule: SES for simple agreements, AES for anything involving HR, real estate, finance, QES only when the law requires it.

Common mistakes

• Systematically taking QES "to reassure ourselves": unnecessary friction for the signer, high cost, often over-dimensioned.

• Sticking to SES for everything: in the event of a dispute over an employment contract, the lack of strong authentication can weaken the evidence.

• Confusing validation and signature: an acknowledgement of receipt is not a signature.

How Certyneo helps you

Certyneo natively supports simple (SES) and advanced (AES) levels, with dual email + SMS OTP via Twilio Verify for AES. For cases requiring QES, Certyneo interfaces with several qualified European providers (Docaposte Certigna, Universign, CertEurope) to trigger qualified signature without changing tools.

You can define the signature level document by document based on stakes — or by template if you have industrialised a process.

Discover the Certyneo electronic signature solution

FAQ

Can I mix levels in the same envelope?

Yes. A multi-document envelope can include a quotation signed in SES and a contract signed in AES, for example. Each signer sees the authentication adapted to the document they need to sign.

Is advanced signature recognised internationally?

Within the EU yes, under the eIDAS mutual recognition principle. Outside the EU, recognition depends on the local legal framework — to be verified according to the jurisdiction concerned.

Do I need a personal certificate to sign in AES?

No. AES can be obtained without a prior personal certificate thanks to double OTP. This is what makes AES very accessible, whereas QES requires a qualified certificate.

Is qualified signature mandatory for an employment contract?

No. The employment contract accepts advanced signature (AES), which already offers strong presumption of validity. For more details, see electronic signature of employment contract.

How do I verify the level of a signed document?

Open the PDF in Adobe Acrobat Reader: the signature properties display the level, signer and timestamp. You can also use an online verifier.

Conclusion

Choosing the right level of electronic signature means finding the balance between evidential value and friction for the signer. Start simple, move up a notch when the legal stakes require it.

Try Certyneo to send, sign and track your documents online simply, quickly and securely.